Is this level of anxiety normal for you? You are worried far more than you should be.
The only thing I'd update from that post - and I'd bet Dr. Handsfield would agree - is the not seeing STDs go "either way". We now know that about 50% of all new genital herpes infections are genital hsv1, the result of someone with oral hsv1 giving someone oral sex.
However, we know that because of better testing and awareness, not because it's happening that much more.
Herpes still doesn't go from the genitals to the mouth nearly as easily as it does the other way around.
Herpes has site preferences - hsv1 prefers the mouth, and hsv2 prefers the genitals. When herpes is in it's preferred site, it is more active - it recurs more often, sheds more often, and therefore transmit more often.
If someone has genital herpes type 1, it rarely sheds, rarely recurs and therefore rarely transmits outside of symptoms. This is true for transmission to the mouth or genitals.
If someone has ghsv2, it is more active, but oral hsv2 still remains uncommon.
For other STDs, it is still uncommon to get anything from oral sex on a vagina. Nothing goes in your throat like giving oral sex to a penis, making transmission less likely.
Syphilis is a possibility, but a chancre needs to be present in order to transmit.
A canker sore doesn't resemble herpes. Your doc is correct.